European Commission Vice President Maros Sefcovic addresses a news conference on European Aviation Strategy at the European Commission headquarters in Brussels, Belgium, December 7, 2015. REUTERS/Francois Lenoir

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BRUSSELS (Reuters) - European Commission Vice President Maros Sefcovic said he will visit Kiev on Friday to discuss energy reforms and lay the groundwork for trilateral talks with Ukraine and Russia that he hopes will help ensure uninterrupted gas supplies in the winter.

The European Union relies on Russia for around a third of its gas. More than half of that arrives via Ukraine, but since ties between Russia and Ukraine hit rock bottom over Moscow's annexation of Crimea from Kiev in 2014, the potential for disputes over pricing and other issues has accelerated.

"Despite a very difficult situation, especially in east Ukraine, the transit route through Ukraine has been working well. We consider it a priority that this route is fully operational this winter as well," Sefcovic told reporters.

He said he would discuss the issue with Ukrainian officials, including the prime minister and energy minister, in Kiev on Friday. He said Ukrainian authorities were in favor of holding trilateral talks but Russia had yet to answer his letter outlining such a proposal.

"These talks have always been about additional legal and political certainty that the three parties will work on this together," he said. Clarifying pricing, financial assistance to cash-strapped Ukraine and delivery points would be other key elements of the three-way talks, he said.

Disputes over pricing and political rows in the past have led to cuts in Russian deliveries for Ukraine as well as for the EU. The European Commission has stepped in on some occasions, brokering agreements to help resume supplies.

Sefcovic praised Ukrainian Prime Minister Volodymyr Groysman's government for showing commitment to reforms in the former Soviet state, which is struggling with a weak economy and endemic corruption, on top of the military conflict.

Sefcovic said further reforms on independent energy and utilities regulators, as well as the electricity market were crucial for unlocking more Western funds to modernize the sector and he hoped Kiev will pass them quickly.